Change the departure date, the Booking Number(PNR): DCAQ65

I will arrive at Milan on Sep 24th 19:00 sharp, the last train to Vicenza is 20:35 on that day, i dont think i can make it on time. Would like to change schedule, should i buy 4 new ticket on 26th sep from Milan to Vicenza, and change the ticke that i alreday bought on Oct 2nd to Oct 4th? the Booking Number(PNR): DCAQ65